Methods of forming wire interconnect structures

ABSTRACT

A method of forming a wire interconnect structure includes the steps of: (a) forming a wire bond at a bonding location on a substrate using a wire bonding tool; (b) extending a length of wire, continuous with the wire bond, to another location; (c) pressing a portion of the length of wire against the other location using the wire bonding tool; (d) moving the wire bonding tool, and the pressed portion of the length of wire, to a position above the wire bond; and (e) separating the length of wire from a wire supply at the pressed portion, thereby providing a wire interconnect structure bonded to the bonding location.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/298,406, filed Oct. 20, 2016, which is a continuation of U.S. patentapplication Ser. No. 14/413,475, filed Jan. 8, 2015, now U.S. Pat. No.9,502,371, which is a U.S. national phase application of InternationalApplication No. PCT/US2013/048860, filed Jul. 1, 2013, which claims thebenefit of U.S. Provisional Application No. 61/672,449, filed Jul. 17,2012, the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to semiconductor packaging, and moreparticularly, to improved methods of forming wire interconnectstructures.

BACKGROUND OF THE INVENTION

A wire bonder (i.e., wire bonding machine) may form wire loops betweenrespective locations to be electrically interconnected. Exemplary wirebonding techniques include ball bonding and wedge bonding. Steps in aball bonding application include: bonding a free air ball to a firstbond location (e.g., a die pad of a semiconductor die); extending alength of wire continuous with the bonded free air ball to a second bondlocation (e.g., a lead of a leadframe); and bonding the wire to thesecond bond location, thereby forming a wire loop between the first bondlocation and the second bond location. In forming the bonds between (a)the ends of the wire loop and (b) the bond sites (e.g., die pads, leads,etc.) varying types of bonding energy may be used including, forexample, ultrasonic energy, thermosonic energy, thermo-compressiveenergy, amongst others.

Wire bonding machines have also been used to form wire contacts andinterconnects having a free end for a number of years. For example, U.S.Pat. No. 5,476,211 to Khandros discloses forming such conductivecontacts using ball bonding techniques. However, conventional techniquesof forming such wire contacts and interconnects suffer from a lack ofconsistency (e.g., height consistency, shape consistency, etc.) andundesirable shapes of the wire contacts and interconnects.

Thus, it would be desirable to provide improved methods of forming wireinterconnect structures.

SUMMARY OF THE INVENTION

According to an exemplary embodiment of the present invention, a methodof forming a wire interconnect structure includes the steps of: (a)forming a wire bond at a bonding location on a substrate using a wirebonding tool; (b) extending a length of wire, continuous with the wirebond, to another location; (c) pressing a portion of the length of wireagainst the other location using the wire bonding tool; (d) moving thewire bonding tool, and the pressed portion of the length of wire, to aposition above the wire bond; and (e) separating (e.g., stretching andtearing) the length of wire from a wire supply at the pressed portion,thereby providing a wire interconnect structure bonded to the bondinglocation.

According to another exemplary embodiment of the present invention, amethod of forming a wire interconnect structure, the method comprisingthe steps of: (a) forming a ball bond at a bonding location on asubstrate using a wire bonding tool; (b) extending a length of wire,continuous with the ball bond, to another location; (c) pressing aportion of the length of wire against the other location using the wirebonding tool to partially cut a portion of the length of wire; (d)moving the wire bonding tool, and the partially cut portion of thelength of wire, to a position above the wire bond; (e) extending anadditional length of wire from the wire bonding tool, and above thepartially cut portion of the length of wire; and (f) separating thelength of wire from a wire supply at the partially cut portion, therebyproviding a wire interconnect structure bonded to the bonding location,the wire interconnect structure extending substantially vertical abovethe wire bond.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is best understood from the following detailed descriptionwhen read in connection with the accompanying drawings. It is emphasizedthat, according to common practice, the various features of the drawingsare not to scale. On the contrary, the dimensions of the variousfeatures are arbitrarily expanded or reduced for clarity. Included inthe drawings are the following figures:

FIGS. 1A-1I are block, side view diagrams illustrating formation ofvertical wire interconnects in accordance with an exemplary embodimentof the present invention; and

FIG. 2 is a block, side view diagram illustrating formation of verticalwire interconnects on a substrate in accordance with another exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “interconnect structures” or “wire interconnectstructures” are intended to refer to conductive structures that may beused to provide any type of electrical interconnection (e.g., atemporary interconnection as in a contact used for testing, a permanentinterconnection as in a semcionductor package interconnect, etc.).

FIGS. 1A-1I illustrate a method of forming one or more wire interconnectstructures in accordance with an exemplary embodiment of the presentinvention. As illustrated in FIG. 1A, free air ball 106 is seated at thetip of bonding tool 104 (e.g., wire bonding tool 104) with wire 110extending upwardly through a bore, or the like, in wire bonding tool 104and through open wire clamp 108. Wire bonding tool 104 and wire clamp108 are carried by a common bond head assembly (not shown) and as such,move together, for example, in a vertical Z axis. As will be understoodby those skilled in the art, free air ball 106 is formed on an end ofwire 110 that hangs below the tip of bonding tool 104 using anelectronic flame-off device or the like (not shown). It will beunderstood that, many elements are omitted from the simplified views ofFIGS. 1A-1I (e.g., an ultrasonic transducer carrying bonding tool 104,etc.).

After free air ball 106 is formed, wire 110 is drawn upwards (e.g.,using a vacuum control tensioner or the like) such that free air ball106 is seated at the tip of bonding tool 104 as shown in FIG. 1A. Wirebonding tool 104 and wire clamp 108 are positioned over substrate 100.As will be appreciated by those skilled in the art, substrate 100 may beany type of element to which a wire interconnect may be bonded.Exemplary substrates include leadframes, semiconductor die, BGA (ballgrid array) package elements, flip chip elements, package-on-package(POP) elements, etc. Bonding location 102 may be any type structureconfigured to receive a wire interconnect. For example, if substrate 100is a semiconductor die then bonding location 102 may be a die pad. Otherexemplary bonding locations include leads, circuits traces, etc.

As shown in FIG. 1A, bonding tool 104 and wire clamp 108 are then moveddownwardly, as at the arrows in a downward Z direction, towards bondinglocation 102 (e.g., along with other elements of the bond headassembly). As illustrated in FIG. 1B, bonding tool 104 and wire clamp108 are lowered and free air ball 106 contacts bonding location 102 andwill form a ball bond using, for example, bonding force, ultrasonicenergy, and heat (e.g., a heat block positioned below substrate 100, notshown). As illustrated in FIGS. 1C-1D, ball bond 112 has now beenformed, and bonding tool 104 and wire clamp 108 (in an open position)are moved upwardly while extending a length of wire 114 from ball bond112 towards another location 116. Length of wire 114 is continuous withball bond 112. Length of wire 114 may be extended in a single step, or aplurality of steps and associated motions, as desired. The motions usedto extend length of wire 114 may be similar to conventional loopingmotions used to extend a wire loop from a first bond location to asecond bond location; however, the portion of wire 114 adjacent tip 120of bonding tool 104 is not ultrasonically bonded/welded to anotherlocation 116. Rather, a predetermined level of bond force (e.g., likelywithout ultrasonic energy), is applied to tip 120 of wire bonding tool104 to press the portion of wire 114 against other location 116 (e.g.,see FIG. 1D). In another example, rather than applying a predeterminedamount of bonding force, wire bonding tool 104 is moved to apredetermined position such that a bond force is applied to press theportion of wire 114 against other location 116. Regardless of whetherthe bond force is applied in a force controlled mode, a positioncontrolled mode, or other mode of operation—this pressing may “deform,”or partially cut, pressed portion 118 of wire 114 beneath tip side 120 aof bonding tool 104, for example, shown as deformed/cut wire portion118. As provided above, deformed/cut wire portion 118 has not beenbonded/welded to another location 116. Rather, it may be temporarilystuck to another location 116 during the formation of deformed/cut wireportion 118.

As illustrated in FIG. 1E, wire bonding tool 104 and wire clamp 108(e.g., in a closed position, but may be open if desired) have beenraised to a position above ball bond 112 with wire 110, havingdeformed/cut wire portion 118, continuous with ball bond 112. Such aposition may be considered to be a top of loop (i.e., TOL) position inconventional wire looping terminology.

At FIG. 1F wire clamp 108 has been moved to an open position, and wirebonding tool 104 and open wire clamp 108 are being raised, as at thearrows in an upward Z direction, to pay out another portion of wire 114′(e.g., a tail length of wire 114′) from wire bonding tool tip 120 thatis continuous with deformed/cut wire portion 118. For example, wireportion 114′ may become a wire tail for a subsequent free air ball. Asmore clearly shown in the enlarged portion of the circle below tip 120of bonding tool 104 in FIGS. 1E-1F, pressed wire portion 118 of wire 110may be a partial cut in wire 110, and separates wire portions 114, 114′.As illustrated in FIG. 1G, wire clamp 108 is closed over an upperportion of wire 110 and, as illustrated in FIG. 1H, wire bonding tool104 and wire clamp 108 are then raised as at the arrows in an upward Zdirection to separate wire 110 proximate deformed/cut wire portion 118to form wire interconnect structure 122. The enlarged portion of thecircle below the tip of wire bonding tool 104 more clearly shows thatwire interconnect structure 122 (separated from wire portion 114′) mayhave an upper tapered, or sharp, end 124. FIG. 1I illustrates substrate100 with other wire interconnect structures 122 formed on additionalbonding locations 102 by the repeating of the method described above. Asillustrated, wire interconnect structures 122 may be vertically erect,or substantially so.

As described above in connection with FIG. 1D, a portion of wire 114 ispressed against another location 116. In the embodiment of FIGS. 1A-1H,another location 116 may be a portion of substrate 100 (e.g. a surfaceportion of substrate 100, etc.). However, it may be appreciated by thoseskilled in the art that any location may be used for another location116. For example, as illustrated in FIG. 2, and according to anotherembodiment of the present invention, the pressing of wire portion 118(for some, or all, of wire interconnect structures 122 to be formed onsubstrate 100) may occur at a location other than substrate 100 (e.g.,on another substrate or structure), such as at anotherlocation/substrate 200 shown in FIG. 2 that is not (directly) part ofsubstrate 100.

Wire interconnect structures formed in accordance with the presentinvention may have improved consistency in height and resultant wiretail lengths, as well as increased efficiency in production (e.g., anincrease in unit per hour produced).

Wire interconnect structures formed in accordance with the presentinvention may be used, for example, as contact structures in probecards, as interconnects between die in stacked die applications, asinterconnects in flip chip applications, as interconnects in throughsilicon via or through mold via applications, as interconnects betweenpackages in POP (package on package) applications, amongst others.

Although the present invention has been described primarily with respectto certain exemplary method steps in a predetermined order, it is notlimited thereto. Certain of the steps may be rearranged or omitted, oradditional steps may be added, within the scope of the presentinvention.

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

What is claimed:
 1. A method of forming a wire interconnect structure,the method comprising the steps of: (a) forming a wire bond at a bondinglocation on a substrate using a wire bonding tool; (b) extending alength of wire, continuous with the wire bond, to another location; (c)pressing a portion of the continuous length of wire against the otherlocation using the wire bonding tool, thereby partially cutting theportion of the continuous length of wire without ultrasonically bondingthe portion of the continuous length of wire to the other location; (d)moving the wire bonding tool, and the pressed portion of the length ofwire, to a position above the wire bond; and (e) separating thecontinuous length of wire from a wire supply at the pressed portion,thereby providing a wire interconnect structure bonded to the bondinglocation, wherein the wire interconnect structure extends substantiallyvertical above the wire bond.
 2. The method of claim 1 wherein thepressing step partially cuts the portion of the length of wire to form apartially cut portion of the continuous length of wire.
 3. The method ofclaim 1 further comprising a step of forming a free air ball that isused to form the wire bond in step (a).
 4. The method of claim 3 whereina bonding force and ultrasonic energy are used in forming the wire bond.5. The method of claim 1 wherein a bond force is used in the pressingstep (c).
 6. The method of claim 5 wherein ultrasonic energy is not usedwith the bond force in the pressing step (c).
 7. The method of claim 1further comprising the step of: (d1) extending an additional length ofwire from the bonding tool, and above the pressed portion of thecontinuous length of wire between steps (d) and (e).
 8. The method ofclaim 7 further comprising the step of closing a wire clamp against anupper portion of wire after step (d1) and before step (e).
 9. The methodof claim 8 wherein the separating of step (e) includes raising theclosed wire clamp and the wire bonding tool in separating the continuouslength of wire from a wire supply at the pressed portion.
 10. The methodof claim 1 wherein steps (a)-(e) are repeated to form a plurality ofwire interconnect structures.
 11. The method of claim 1 furthercomprising the step of using the wire interconnect structure toelectrically connect the substrate with another, adjacent substrate. 12.The method of claim 1 wherein the other location is on the substrate.13. The method of claim 1 wherein the other location is not on thesubstrate.
 14. The method of claim 1 further comprising the step ofclosing a wire clamp against an upper portion of wire after step (d) andbefore step (e).
 15. A method of forming a wire interconnect structure,the method comprising the steps of: (a) forming a ball bond at a bondinglocation on a substrate using a wire bonding tool; (b) extending alength of wire, continuous with the ball bond, to another location; (c)pressing a portion of the length of wire against the other locationusing the wire bonding tool to partially cut a portion of the length ofwire, thereby partially cutting the portion of the continuous length ofwire without ultrasonically bonding the portion of the continuous lengthof wire to the other location; (d) moving the wire bonding tool, and thepartially cut portion of the length of wire, to a position above theball bond; (e) extending an additional length of wire from the wirebonding tool, and above the partially cut portion of the length of wire;and (f) separating the length of wire from a wire supply at thepartially cut portion, thereby providing a wire interconnect structurebonded to the bonding location, the wire interconnect structureextending substantially vertical above the ball bond.
 16. The method ofclaim 15 further comprising a step of forming a free air ball that isused to form the ball bond in step (a).
 17. The method of claim 15wherein a bonding force and ultrasonic energy are used in forming theball bond.
 18. The method of claim 15 wherein a bond force is used inthe pressing step (c).
 19. The method of claim 18 wherein ultrasonicenergy is not used with the bond force in the pressing step (c).
 20. Themethod of claim 15 further comprising the step of closing a wire clampagainst an upper portion of wire after step (e) and before step (f). 21.The method of claim 15 wherein steps (a)-(f) are repeated to form aplurality of wire interconnect structures.
 22. The method of claim 15further comprising the step of using the wire interconnect structure toelectrically connect the substrate with another, adjacent substrate. 23.The method of claim 15 wherein the other location is on the substrate.24. The method of claim 15 wherein the other location is not on thesubstrate.